1. Field of the Invention
The present invention relates to an engine cylinder liner construction in which a cylinder liner is cast into a cylinder block, and more particularly to an engine cylinder liner construction in which projections are formed on an outer surface of the cylinder liner so as to strengthen the adhesion properties of the cylinder liner to the cylinder block.
2. Description of the Related Art
There have been adopted lots of engines in which a cylinder block main body is made of aluminum alloy with a view to reducing the weight thereof. Incidentally, in the aluminum alloy-made cylinder block of this type, in many cases, separate cylinder liners of cast iron or steel alloy are integrally cast into the cylinder block at the time of producing a cylinder block main body with a view to increasing wear resistance against pistons. In this case, cylinder liners are cast or pressed into the cylinder block. An example of such a pressing process is disclosed in JP-UM-A-3-89955.
Incidentally, in a case where the casting process is adopted to produce engines in which cylinder liners are cast into a cylinder block, when casting cylinder liners made of a different material into the cylinder block, due to the difficulty in making the cylinder block to completely adhere to the cylinder liners at the time of producing a cylinder block main body, minute gaps are produced between the cylinder block and the cylinder liners with time, and there are caused problems of reduction in accuracy of the roundness of the cylinder liner and of reduction in cooling performance thereof.
In a cylinder block disclosed in JP-A-2002-97998, for example, the adhesion properties of cylinder liners to a cylinder block are attempted to be secured by casting into the cylinder block cylinder liners each having a large number of spines or prickles which are formed on an outer surface thereof. Note that in this cylinder block, spines are eliminated between the adjacent cylinder liners so as to suppress the casting failure in facing gaps between the adjacent cylinder liners to thereby prevent the reduction in rigidity.
Incidentally, a cylinder head is superposed on the cylinder block via a gasket, and both the cylinder head and the cylinder bock are fastened together with bolts. As this occurs, in the cylinder block 100 shown in FIG. 6A, a relatively large fastening load W is applied to an upper end face fh which faces the cylinder head 120 of a cylinder liner 110 in which a piston is fitted in a press contact direction via the gasket 130. In this case, while a casting portion 140 where the cylinder liner 110, which is spiny, is cast, can function to secure the adhesion properties between the casting portion 140 and the cylinder liner 110, there exists a possibility that a gap is produced with time in a joint portion b between the casting portion 140 on the cylinder block 100 side and the cylinder liner 110 due to the fastening load w so applied and fluctuation in the gas pressure received by the cylinder head 120, and with the production of such a gap in the joint portion b, a damaged portion C tends to be easily produced in the gasket 130 in association with the gap production. Moreover, a crack 170 tends to be easily produced in a distal end of a needle-like projection 180 which is formed in the vicinity of the end portion of the cylinder liner 110 which faces the cylinder head 120 in association with the concentration of stress thereat, and this tends to produce a damaged portion C in a portion of the gasket 130 which faces the cracks so produced in the end portion of the cylinder liner 110, resulting in an easy-occurring problem that the sealing properties are reduced.